Chromium plated article and method of producing same



. mium plating which entails a minimum amount Patented July 26, 1938 CHROMIUM PLATED ARTICLE AND METH D OF PRODUCING SAME Philip J. Ritzenthaler and Patrick J. Shcehan, Milwaukee, Wis assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware No Drawing. Application October 11, 1934,

Serial No. 747,888

4 Claims. (01. 204-196 This invention relates to chromium plated ar for the plating of articles made of die casting ticles and a method of producing such articles. metals. It produces thereon the same high lus- An object of nie inventionis to provide a chrotre of the chromium coating as is produced on mium surface of a veryhigh lustre'. articles made of other metals, and affords better Another object is to provide a simple and inprotection against corrosion than prior methods. expensive method for producing a chromium de- In accordance with the present invention, the posit of high lustre. V article which is to be provided with a chromium Another object is to provide a chromium desurface is first electroplated wltha layer of cadposit which aifords a maximum protection from mium. The cadmium is then dipped in a suito si n, able brightening solution, whereupon a layer of Another object is to provide a method of chronickel and thereafter a layer of chromium is-deposited thereon. With this process it is only necessary to polish thebase, while no polishing operations are required after the deposition of the intermediate metal layers. The resulting surface has a very high lustre, which is only equalled with the old method by the exercise of the utmost care during every step.

The process is preferably carried out in the folof material, labor, and time for a given thickness of protective coating.

Another object is to provide an efllcient method of chromium plating for die castings. Another object is to provide a dipping solution suitable for employment in the production of chromium deposits of the aforementioned character. lowing manner:

Other objects and advantages will hereinafter The article which is to be chromium plated is appear. thoroughly cleaned and polished to the desired smoothness. manner with a layer of cadmium. The cadmium plating bath should have a concentration of 2 to 3 ounces of metallic cadmium per gallon of solution.

After the cadmium has been deposited the article is preferably dipped into a solution of 5 to of acetic acid and .5% iodine, having added thereto 2 to 5% of potassium iodide as a stabilizing agent. This dip produces a bright lustrous In the heretofore known method of chromium plating of articles, a base surface was first polished to the desired smoothness. Thereafter, a heavy layer of copper was deposited on said surface and the copper deposit was again polished to a high lustre. Thereupon a coating of nickel was deposited on the polished copper, and the nickel in turn was polished to high lustre, after which a coating of chromium was deposited on the nickel. This chromium layer then presented a surface of high lustre. This,process is very wasteful in material, labor, and time, on account of the repeated polishing operations required for the intermediate layers of metal. Relatively thick coats of the various metals must be deposited so as to leave a sufllcient amount after the polishing operation has .removed some of the metal. The repeated polishing consumes considerable time and labor, all of which makes the plating of chromium expensive.

The chromium plating of die-cast articles which are made of an alloy having a zinc base 'was particularly unsatisfactory, because it is practically impossible or at least very difllcult to deposit a well-adhering layer of copper on the die metal with the result that the finished chromium plated article peels and soon loses its good appearance.

The method of plating which is the subject of the present invention avoids the necessity of p01- .ishing the intermediate layers of metal and yet results in a bright chromium surface of high lustre. The method is also particularly suitable prolonged for any length of time, provided that the cadmium layer previously deposited is not completely removed from the base surface. Hence, the process does not require extreme care when carried out. The resulting cadmium surface is an exact duplicate of the polished surface of the base, but having even a higher lustre than the latter. Thereafter the article is washed in water and then put into the nickel bath. The

layer of nickel which isdeposited need only be very thin. After again washing the article it is plated with a. layer of chromium by the usual method.

The final chromium surface is bright and of high lustre and reflecting power. I

In the above described solution, bromine may be substituted for the iodine as follows:

chloric acid .5% and postassium bromide '2 to 5%.

The process when using the bromine solution is the same as that used when employing the Thereafter it is plated in the usual surface on the cadmium. The dipping may be Acetic acid 540%, bromine .1 to 2%, hydroknown heretofore, but most of these solutions were not suitable for chromium plating, while others produced a metal surface of insuflicient lustre to insure a mirror-like surface on the subsequently deposited chromium. Hence it has always been found necessary heretofore to polish the intermediate metal deposits. A dipping solution which has been used in the past to produce a high lustre on cadmium consists of chromic acid and sulphuric acid in which the ratio of chromic acid to sulphur acid radical is between 20:1 and 40:1. However, this solution leaves a chromate film which has been formed during the .chror'nic acid dip,which film prevents a good adherence of the subsequent metal layers to the cadmium and retention of the original lustre. We have found that by following the chromium dip aforedescribed with another clip .of short duration in a hydrochloric acid solution, the film is removed. The article is there after washed in water and then put into the nickel bath and. the subsequent treatment is the same as that aforedescribed in connection with the iodine dip.

What we claim as new and desire to secure by Letters Patent is:

. 1. An electroplated chromium finished article having a natural high lustre, which comprises a cadmium electroplated smooth base, the cadmium surface thereof being chemically brightened but 3. In a process of electroplating a base having a smooth surface, the steps of electrodepositing on the base a layer of cadmium, dipping the cadmium coated base in an acetic acid solution containing one 01' the group consisting of iodine and bromine to obtain a high lustre surface, electrodeppsiting on the cadmiuni a layer of nickel and electrodeposlting on the nickel a layer of chromium to obtain a chromium surface of high lustre, all without any mechanical polishing or any dipping other than that specificed.

4. In a process of electroplating a base having a smooth surface, the steps-of depositing on the base a layer of cadmium, finishing the cadmium for high surface lustre while preserving a layer of the cadmium by dipping into an acetic acid solution containing a halogen, electrodeposlting on the dipped cadmium a layer of nickel having a natural surface of high lustre and electrodepositing on the natural surface of the nickel a layer of chromium having a natural surface of high lustre.

PHILIP J. RITZENTHALER. PATRICK J. SHEEHAN. 

